1. Field of the Invention
The present invention relates to a technique for implementing illumination control of lighting system for a vehicle while estimating the shape of a driving path ahead of the cruising vehicle.
2. Description of the Related Art
The following types of vehicle driving support systems are known with regard to the light distribution control of vehicle headlamps according to a driving path on which a cruising vehicle runs.
(I) A type in which an illumination control is performed while interlocking with a steering state of the vehicle; and
(II) A type in which an automatic transmission control systems or traction control systems and vehicle stability control systems are employed, performing the relevant controls based on data on the shape of a road path obtained from vehicle navigation systems.
Firstly, in the type (I), a system is raised in which a steering angle is detected using, for example, a steering sensor, so that the illuminating direction of the headlamp is controlled so as match the traveling conditions of the vehicle and the system exhibits good controllability while driving on a curved path.
Secondly, in the type (II), namely, the lighting systems for the vehicles which enables the light distribution control of vehicle headlamps according to a driving path on which the cruising vehicle is traveling, there is known, for example, a type of lighting system in which the illumination range is controlled while determining a distance to a bend ahead of the cruising vehicle on the road on which it is driving or the direction of the bend based on the map information and information on the location of the cruising vehicle on the map, such as disclosed in JP-A-2-296550.
Alternatively, a system is known in which a beam control is performed using as a target position a position where the cruising vehicle is estimated to arrive after a predetermined period of time has elapsed from the current point in time, such as disclosed in JP-A-2002-52975.
In the lighting system like this, the following become critical in order to implement accurate illumination controls.                To obtain detailed information such as on the shape of a road path extending ahead of the vehicle; curved or bent, and the position of intersections and the like emerging ahead of the vehicle; and        To obtain positional information on starting points and terminating points (or exit points) on curved and bent paths.        
In addition, in configurations which make use of navigation systems, road-to-vehicle communication systems and the like, the shape of a road path can be estimated from position data of nodes (road notation points on a road map database) existing on the traveling path of the cruising vehicle through a 3-point arc interpolation process or the like.
However, the conventional systems have the following drawbacks.
In the type (I), for example, since a starting point of a curved or bent path can not be known in advance, in the event that there occurs a delay in performing an illumination control, there are caused problems that the field of vision in front of the driver is affected and that the driver is made to feel a feeling of physical disorder.
Further, in the type (II), when attempting to calculate shape data on the shape of a road path and starting points and terminating points of curved paths using geometric or shape engineering methods, with no sufficiently accurate map-matching, measurement of coordinates of the current position and road map database, it is difficult to obtain the shapes of curved and bent paths accurately. This causes a problem that sufficient accuracy cannot be ensured as to control timings of the illuminating direction. Namely, an illumination control that does not match the actual conditions is performed due to the lack of accuracy, causing a risk that the driver has to feel a feeling of physical disorder or uncomfortableness due to time lag in control timing, and this causes problems that not only driving is disturbed but also other road users are affected.
When driving on a curved or bent path, while it is preferable from the viewpoint of control to grasp a starting point and a terminating point of the curved or bent path, the processing and storage capacities of a CPU (central processing unit) that is used in the system needs to be increased. For example, when adopting an interpolation processing using spline curves and free curves, it becomes necessary to deal with an increase in calculation volume necessary for calculation and determination of the shape of a road path or a problem that the application of spline curves is made inappropriate depending on the number and arrangement of node points according to the shape of a road path (for example, in a road shape which is made up of winding paths and bent paths, in case the number of node points and the degree of an interpolation function are inappropriate, there are caused irregular amplitudes and an interpolation curve becomes wavy).
In a case where the driver's visual recognition is critical as with the light distribution control of headlamps, high accuracy is generally required, and in the event that the determination of the shape of a road path fails, there may be caused a risk that an illumination control that does not match actual conditions is performed.
For example, when controlling the light distribution of the headlamps based on the results of a calculation of the radius of the shape of the road path ahead of the vehicle through the 3-point arc interpolation, the following methods are raised.
(1) A method for estimating a position reached by the cruising vehicle in a predetermined period of time and controlling the direction of illumination beams using the position so estimated as a gazing point; and
(2) A method for controlling the direction of illumination beams using a clipping point of a curved path as a gazing point.
For examples, FIGS. 23, 24 and 25 illustrates ways in which the vehicle runs, respectively, on a bent path, a curved path and at an intersection, in which N1 to N4 denote node points. In addition, in the drawings, symbols shown as something like a home plate in solid lines denote an actual current position “P” of the vehicle (a pointed portion of the symbol denotes a traveling direction of the vehicle), and symbols shown as something like a home plate in dotted lines denote the current position “Q” of the vehicle (a pointed portion of the symbol denotes a traveling direction of the vehicle) that is recognized on a navigation system. In each drawing, the positions P and Q are shown as not coinciding with each other.
In FIG. 23, a node N2 is a bending point, and the position Q is located slightly forward of the vicinity of a node N1. An arrow a followed by a dotted line indicates the traveling direction of the vehicle, and an arrow b followed by a dotted line indicates the illuminating direction of the headlamps. Then, the position P is located slightly forward of the vicinity of the node N2, and an arrow A followed by a solid line indicates the traveling direction of the vehicle, whereas an arrow B followed by a solid line indicates the illuminating direction of the headlamps. In addition, an arrow C followed by a solid line indicates an ideal illuminating direction of the headlamps at the position P.
A deviation between the actual vehicle position and the vehicle position on the map (an imaginary current position) emerges as a deviation between the illuminating directions, and in this example, an illuminating direction that is calculated at the position Q becomes the illuminating direction indicated by the arrow b followed by the dotted line and the illuminating direction becomes the direction indicated by the arrow B followed by the solid line at the actual position P. In case the positions P and Q had coincided with each other, the illuminating direction at the position P should have become the direction indicated by the arrow C followed by the solid line, however, since there is caused a deviation between both the positions in reality, there is caused a problem that the illuminating direction is controlled to be directed in a direction deviating from the ideal direction of the arrow C at the position P, that is, the direction indicated by the arrow B followed by the solid line.
Note that while in this example, a case is conceived in which the position Q is behind the position P as viewed in the traveling direction of the vehicle, a deviation from the ideal illuminating direction occurs even when the position Q is ahead of the position P.
In addition, in FIG. 24, a node N2 constitutes a starting point of a curved path, a position Q is slightly behind the node N2, which is located before an entry point to the curved path, and the orientations of arrows a and b which are followed by dotted lines, respectively, are in such a condition that they coincide with each other. Then, a position P is slightly behind the vicinity of a node N3, the orientations of arrows A and B which are followed by solid lines, respectively, coincide with each other, and there is occurring a large deviation between the orientations of the arrows A and B and an arrow C followed by a solid line when they are compared with each other (namely, the deviation from the arrow C followed by the solid line becomes larger as the curving radius of the curved path becomes smaller).
In FIG. 25, a position Q constitutes a point before an entry point into the intersection, and the orientations of arrows a and b which are followed by dotted lines, respectively, are in such a condition that they coincide with each other. Then, a position P constitutes a point after the entry into the intersection, and orientations of arrows A and B which are followed by solid lines, respectively, coincide with each other, there occurring a large deviation between the orientations of the arrows A and B, and an arrow C followed by a solid line which indicates an ideal orientation (a direction which the vehicle takes when it turns left) when they are compared with each other.
The deviations described above can be dealt with by improving the map-matching accuracy. Namely, the definition of shape characteristics is accurately implemented by analyzing the shape of the driving path in detail and orientation sensor information and information on the distance covered by the vehicle are obtained, so that segments covered by the vehicle may be collated with shapes of driving paths on the map one by one. In this case, however, there occurs a problem that the calculation and processing capacities of the system need to be increased largely or an unrealistically long processing period of time is required for a practical use.
Further, when applying the 3-point arc interpolation to these controls in the same way, for example, in the event that a phenomenon occurs in which the direction of illumination beams changes momentarily (quick drift of beams), it is concerned that the field of vision of the driver is affected or the driver of an oncoming vehicle is dazzled.
FIG. 26 shows an example of the shape of a road path resulting from connecting node points denoted by N1 to N4, and the resulting shape indicates a curved path of an S-shape.
The occurrence of the phenomenon is attributed to the fact that a difference is generated at all times between a radius R1 resulting from a calculation using nodes N1, N2, N3 situated at three points selected based on the current position of the vehicle as a reference and a radius R2 resulting from a calculation using nodes N2, N3, N4 which constitute next three points (in this example, the direction in which the road curves is reversed when the Node N2 is passed). It is found out that this phenomenon occurs when an estimated reached position of the cruising vehicle in a predetermined period of time or the clipping point is attempted to be illuminated and when the vehicle is driving on a bending path such as a hairpin bend and is passing a starting point and an exit point of a curved path. In addition, the phenomenon also occurs when the current vehicle position is erroneously recognized or there is caused a large position error due to an inferior map-matching.
In addition, in the type (II), for example, in a case where the shape of the road ahead of the current position of the cruising vehicle is recognized as a bent line using a road map database of the navigation system and an illumination control is performed according to the results of an estimation of the shape of the driving path, a map-matching accuracy and an estimation accuracy of road shapes are regarded as problems. Namely, in the event that the map-matching accuracy is as low as on the order of 10 m and the estimation accuracy of a bending direction of the driving path based on data of the map database is low, it becomes difficult to perform the light distribution control with high accuracy when driving on a curved path or slaloming path (a big problem still remains even if attempting to realize such a highly accurate light distribution control only by enhancing the map-matching and orientation measuring accuracies higher than the current levels).
Consequently, it is difficult to realize the highly accurate light distribution control without a proper illumination control which is performed according to a change in the traveling direction of the vehicle by estimating a shape change point of the driving path when the cruising vehicle is about to enter a curved path, a bent path and an intersection or assurance of high control accuracy.
Thus, it becomes critical to know how to implement a best illumination control of the headlamps within the limit of accuracy that has to be encountered.